As of 5.19.2 or so, lex_stuff may have spaces,
so those need to be skipped as well
Create a new op instead of updating the buffer

The code was updating the buffer of a constop, which as of
5.20 is fatal to do.  Instead, we can generate a new const OP
in its place.
Merge remote-tracking branch 'kappa-pulls/1'

This is https://github.com/kappa/signatures/pull/1:
As of 5.19.2 or so, lex_stuff may have spaces
changelog for RT#95181